JP2017130487A - Millimeter wave and sub-millimeter wave generating device by mixing two-wavelength laser beam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a millimeter wave and sub-millimeter wave generating device using a two-wavelength laser light source, which has a wide output wavelength band and not require a long time for an operation stability.SOLUTION: A millimeter wave and sub-millimeter wave generating device, comprises: a multi-wavelength laser light source having an external part resonator structure; a narrow band wavelength selection device on the optical path; a wavelength selection device; selection wavelength variable means of changing the selection wavelength of the wavelength selection device; and an optical mixer. The multi-wavelength laser light source is a light source that outputs a plurality of laser beams from a center to a band of 0.05 to 3THz. The wavelength selection device is an optical filter selecting the laser beam in a toothed comb shape. The narrow band wavelength selection device selects two spectral lines from the toothed-comb-shaped laser beam. The selection wavelength variable means change a transmission wavelength band of the wavelength selection device. The optical mixture mixes the laser beam of two spectral lines, and generates an electromagnetic wave. The wavelength selection device is constructed so that an optical delay plate is provide in an optical resonator, and controls the optical delay by rotating an axis inclined from an optical axis of a double refraction as a center.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a millimeter wave and submillimeter wave generator by two-wavelength laser light mixing that generates millimeter waves and submillimeter waves from two laser lights.

In recent years, millimeter wave and submillimeter wave technologies are expected to be applied to ultra-high-speed wireless communications and sensing fields. Various sources for these frequencies have been proposed, but large-scale equipment is required, sufficient output cannot be obtained, or the output is limited to pulse waves instead of continuous waves. The wavelength fluctuation of the output wave was too large and there were many practical problems.
Such a problem is expected to be solved by generating a beat signal or a difference frequency by a two-wavelength laser used in the laser radio field. This is a point that a simple apparatus configuration that operates at room temperature can be obtained. When realizing such an apparatus, it is important to develop a laser that can be controlled to oscillate two wavelengths simultaneously. As an apparatus for switching between two wavelengths, there is a laser light source for writing on a CD (compact disc), a DVD (digital versatile disc) or the like. However, even if the output light from these laser light sources is mixed, only radio waves and light with shorter wavelengths than millimeter waves, millimeter waves, and submillimeter waves can be obtained.

  In addition, laser light sources that output multi-wavelength laser light having sidebands with frequency bands of millimeter waves and submillimeter waves have already been realized, and such laser light sources have various wavelengths within the band. It is possible to output laser light simultaneously. For example, a semiconductor laser element having a double hetero structure or a quantum well type semiconductor laser element, and a quantum dot laser element can also be used in recent years.

  By using this, for example, Non-Patent Document 1 reports an example of realizing two-wavelength oscillation at intervals of 90 GHz to 1 THz in an external resonator type wavelength tunable laser using a semiconductor gain chip as shown in FIG. Has been. This example includes a multi-wavelength laser light source including an optical amplifying element 1 of a highly integrated quantum dot optical gain chip and an external resonator. The external resonator is an optical resonator formed by the end face 1 a of the optical amplifying element 1 and the half mirror 5. A narrow band wavelength selector 3 and a wavelength selector 4 using an etalon filter are provided on the optical path of the external resonator, and laser light is output through the half mirror 5 and the lens 6.

  In the above configuration, the wavelength selector 4 and the narrowband wavelength selector 3 are adjusted as shown in FIG. First, a number of spectral lines having a comb-like distribution are selected from the light from the multi-wavelength laser light source by the wavelength selector 4 as shown in FIG. From the large number of spectral lines, two spectral lines are selected by the narrowband wavelength selector 3 as shown in FIG. FIG. 3 shows two actually obtained laser spectral lines. It can be seen that laser light of 1539.73 nm and 1540.44 nm is selected.

  In the above configuration, the interval between the two wavelengths to be output is selected by a method of changing the FSR (Free Spectral Range) by exchanging the etalon filter of the wavelength selector 4. Thus, although it is not impossible to control the wavelength interval without replacing the etalon filter, there are practically difficult points as follows.

A method of changing the FSR of an etalon filter that is possible in the prior art is to change the refractive index of a material used for the etalon by heating, for example, thereby changing the FSR. For this heating, a heater is attached to the etalon filter.
However, for example, the thermal conductivity of silicon dioxide glass used as the material for the etalon filter is orders of magnitude smaller than that of metals, so control due to temperature changes involves thermal drift, which must be slow control. I didn't get it.

  Further, it is known that the transmission wavelength of light can be controlled by rotating the optical axis of the birefringent plate with a lyo filter (Lyot Filter) (Patent Documents 1 and 2). In addition, the wavelength variable rio filter using liquid crystals instead of the birefringent plates (Patent Documents 3 and 4) controls the transmission wavelength of light by controlling the voltage applied to the liquid crystals. It is known that spectral lines can be selected using such a rio filter. However, this corresponds to adjusting the selection wavelength of the narrowband wavelength selector 3 and does not correspond to changing the characteristics of the wavelength selector 4.

JP 2009-69576 A US Patent Publication 2002-0054614 JP 2009-69695 A JP-A-3-282417

Koichi Akabane, Naokatsu Yamamoto, Atsushi Kanno, Toshiaki Umezawa, Tetsuya Kawanishi, Noriyoshi Kanemori, Yuji Takai, "Quantum Dot Dual Wavelength Laser with THz Frequency Separation", 61st JSAP Spring Meeting, 17a- E15-5.

  The refractive index change due to the temperature is very small. For this reason, it has been difficult to change the FSR practically. Also, it takes a long time for the temperature to stabilize, and until then, thermal drift occurs as the temperature rises. May be recognized as a problem.

  Therefore, the present invention realizes a millimeter wave and submillimeter wave generator that has a wide output wavelength band and does not require a long time for stable operation.

A millimeter-wave and submillimeter-wave generator using the two-wavelength laser light source of the present invention includes a multi-wavelength laser light source having an external resonator configuration, a narrow-band wavelength selector installed on an optical path in the external resonator, A wavelength selector; a selection wavelength variable unit that changes a selection wavelength of the wavelength selector; and an optical mixer.
Here, the multi-wavelength laser light source is a light source that outputs laser light having a plurality of spectral lines in a band from 50 GHz to 3 THz from the center of the spectrum of the output light, and the wavelength selector includes the multi-wavelength laser light source. An optical filter that selects laser light from a light source in a comb-like shape with respect to wavelength, and the narrow-band wavelength selector selects two spectral lines from the laser light selected in a comb-like shape, The selection wavelength variable means acts to change the transmission wavelength band to the wavelength selector, and the optical mixer mixes the laser light of the two spectral lines, so that the frequency range from 50 GHz to 3 THz. It generates a predetermined electromagnetic wave.

  The wavelength selector is a one-stage or multistage rio filter provided in an optical resonator, the rio filter is a tunable rio filter, and the birefringent plate used in the rio filter is It has an incident surface perpendicular to the optical path in the external resonator, has two axes with different refractive indexes on the incident surface, and has a configuration for manipulating the refractive index of the birefringent plate by the action from the selection wavelength varying means. It may be a thing.

  By obliquely crossing the incident surface of the laser beam to the narrow-band wavelength selector and its incident optical path, the polarization in the direction oblique to the incident optical path is attenuated compared to the polarization in the direction orthogonal to the incident optical path. It is desirable to be a thing.

  By detecting the intensity of the predetermined electromagnetic wave generated from 50 GHz to 3 THz and returning the detection signal to the selected wavelength variable means so that the intensity of the electromagnetic wave becomes a maximum or a predetermined value, By making the transmission characteristic of the wavelength selector follow the transmission characteristic of the narrow band wavelength selector, a stable output can be obtained.

  As the multi-wavelength laser light source, a semiconductor laser element having a double hetero structure can be used. In addition, by using a quantum well type semiconductor laser element with a more limited emission region, laser light with a wider sideband can be obtained. Furthermore, by using a quantum dot laser element with a limited emission region, laser light with a wider sideband can be obtained.

  In the conventional two-wavelength laser light source, only discrete wavelength interval changes due to replacement of the etalon filter or only small wavelength interval changes due to temperature changes have been realized. To be able to change. In addition, a polarizing beam splitter or the like has been realized using a birefringent material, and a highly accurate processing technique has already been established. For this reason, it is possible to realize a two-wavelength light source capable of controlling the wavelength interval over a wide range with high accuracy and almost continuously with the current technical level. Can be expected to occur.

It is a figure which shows the example which implement | achieved 2 wavelength oscillation of 90 GHz-1 THz space | interval in the conventional external resonator type | mold wavelength-tunable laser using a semiconductor gain chip. From the light from the multi-wavelength laser light source, (a) a large number of spectral lines having a comb-like distribution are selected by the wavelength selector 4, and (b) the narrow-band wavelength selector 3 selects 2 from the large number of spectral lines. It is a schematic diagram which shows a mode that a spectrum line of a book is selected. It is a figure which shows that the two laser spectral lines actually obtained with the structure of FIG. 1, the laser light of 1539.73 nm and 1540.44 nm, are selected. It is a figure which shows the Example of this invention. A multi-wavelength laser light source including an optical amplifying element 1 of a highly integrated quantum dot optical gain chip and an external resonator is provided. The external resonator is formed of the end face 1a of the optical amplifying element 1 and the half mirror 5, and an etalon in which a narrow band wavelength selector 3 and a reflective layer serving as an optical resonator are provided on both surfaces of a birefringent material on the optical path. A wavelength selector 4 using a filter is provided, and laser light is input to an optical mixer 8 using a nonlinear optical material, and millimeter waves and submillimeter waves having the difference frequency are output. It is a figure which shows the operation | movement principle of this invention, (a) shows the example using a uniaxial birefringent crystal plate with a birefringence ellipsoid characteristic, (b) shows the normal of a birefringent crystal plate. An example of rotating the wavelength selector 4 around is shown. FIG. 5 is a diagram illustrating a configuration example for adjusting the refractive index of the wavelength selector 4, in which (a) is a configuration for rotating an etalon filter according to a control signal from the etalon controller 22, and (b) is a wavelength selection This is an example in which a liquid crystal retarder type etalon filter is used for the vessel 4.

  Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, devices having the same function or similar functions are denoted by the same reference numerals unless there is a special reason.

  FIG. 4 shows an embodiment of the present invention. A multi-wavelength laser light source including an optical amplifying element 1 of a highly integrated quantum dot optical gain chip and an external resonator is provided. The external resonator is an optical resonator formed by the end face 1 a of the optical amplifying element 1 and the half mirror 5. On the optical path of the external resonator, there are provided a narrow-band wavelength selector 3 and a wavelength selector 4 using an etalon filter provided with reflection layers serving as optical resonators on both sides of a birefringent material. The laser light is input to the optical mixer 8 using the nonlinear optical material via the lens 6 and the millimeter wave and the submillimeter wave having the difference frequency are output.

  The multi-wavelength laser light source is a laser beam having a plurality of spectral lines in a band from 50 GHz to 3 THz from the center of the spectrum of the output light. Millimeter waves and submillimeter waves output from the optical mixer 8 are, for example, , An electromagnetic wave having a predetermined frequency from 50 GHz to 3 THz.

  As the multi-wavelength laser light source, a semiconductor laser element having a double hetero structure can be used. In addition, by using a quantum well type semiconductor laser element with a more limited emission region, laser light with a wider sideband can be obtained. Furthermore, by using a quantum dot laser element with a limited emission region, laser light with a wider sideband can be obtained.

  The narrow-band wavelength selector 3 can select a polarization component in a direction orthogonal to the optical path by arranging the incident surface so as to obliquely intersect the optical path.

  The wavelength selector 4 is an etalon filter using a birefringent material. The birefringent material is used as an optical delay plate and rotated about an axis inclined from the birefringent optical axis to obtain the above-described polarization component. On the other hand, the refractive index can be changed. By changing the refractive index, the FSR can be changed, and the spectral line interval shown in FIG. 2A can be changed.

  In order to change the refractive index in this way, the wavelength selector 4 uses, for example, a uniaxial birefringent crystal plate having a birefringence ellipsoidal characteristic shown in FIG. This birefringent crystal plate is an etalon filter having a plane whose direction is a line (a in the figure) inclined by a predetermined angle θ from the optical axis of the birefringence ellipsoid. In this plane, the refractive index (ne) for extraordinary light and the refractive index (no) for ordinary light are different in each direction, and these directions are orthogonal. Therefore, as shown in FIG. 5B, the propagation delay amount for the polarization component can be changed by rotating the wavelength selector 4 around the normal line. As a result, the FSR of the wavelength selector 4 can be changed. You can adjust it.

  When there is no narrow band wavelength selector 3, comb-shaped spectral lines are obtained by the wavelength selector 4. Therefore, two spectral lines are selected by the narrow band wavelength selector 3 as shown in FIG. The selected two laser beams having the spectral lines are output through the half mirror 5 that forms one end of the external resonator, and enter the optical mixer 8. In the optical mixer 8, a millimeter wave and a submillimeter wave 10 are generated from the laser light of the two selected spectral lines. A part of this millimeter wave and submillimeter wave 10 is branched by the branching device 20, and the etalon controller 22 detects the intensity of the millimeter wave and submillimeter wave, and this strength information is used as a feedback signal. The refractive index of the wavelength selector 4 is adjusted by known nonlinear control (for example, PID control, Proportional-Integral-Derivative Control) so that the detected millimeter wave and submillimeter waves have the maximum or predetermined intensity. . By this feedback control, the frequency of the millimeter wave and submillimeter wave output can be stabilized.

  For the narrowband wavelength selector 3, for example, an oxide dielectric bandpass filter can be used. When this is used, since the transmission band can be easily changed by changing the angle of the incident surface with respect to the optical path, the above two spectral lines can be set to exhibit the same transmission characteristics. Therefore, it is obvious that the feedback signal can be used for the narrowband wavelength selector 3 and automatically controlled so that the selection characteristics are equal to the two spectral lines selected above.

  Thus, the above feedback signal can be applied in the following two ways. First, when preferentially determining the wavelengths of the output millimeter wave and submillimeter wave, it is desirable to automatically adjust the wavelength selected by the narrowband wavelength selector 3 as described above. In order to stabilize the wavelengths of millimeter waves and submillimeter waves, it is desirable to fix the selection wavelength by the narrowband wavelength selector 3 and to automatically control the selection characteristics of the wavelength selector 4 as described above.

  A configuration example for adjusting the refractive index of the wavelength selector 4 is shown in FIG. FIG. 6A shows a configuration in which the wavelength selector 4 shown in FIG. 5B is rotated by an etalon rotation drive device 23 according to a control signal from the etalon controller 22. FIG. 6B shows an example in which a liquid crystal retarder type etalon filter is used for the wavelength selector 4. Also in this case, the birefringence of the etalon filter is controlled according to the control signal from the etalon controller 22.

  As described above, in the present invention, the FSR of the etalon filter element is greatly changed. In order to realize this, a birefringent material such as calcite (calcium carbonate) or rutile is used as the material of the etalon filter element. The birefringent material substrate is a material that exhibits a different refractive index in the substrate surface by appropriately selecting a plane orientation, and is a material often used for a polarization beam splitter or the like. When laser oscillation occurs in the external resonator, the polarization direction is fixed in a predetermined direction. Therefore, when an etalon filter made of a birefringent material is inserted into this resonator, the polarization of laser oscillation feels a refractive index corresponding to the polarization direction, and an FSR corresponding to the refractive index and the thickness of the substrate is obtained. . When the etalon filter is rotated within the substrate surface, the laser light generated by the laser oscillation senses a different refractive index depending on the amount of rotation, and changes the FSR.

  Since the millimeter wave and submillimeter wave generator by the two-wavelength laser beam mixing of the present invention can be realized by the configuration shown in FIG. 4, a portable millimeter wave and submillimeter wave generator can be easily realized.

  In order to obtain high-intensity millimeter waves and submillimeter waves, laser light is incident on the fiber-type optical amplifier before being incident on the optical mixer 8, for example, and is amplified. Incident. Even in this configuration, a portable millimeter wave and submillimeter wave generator can be easily realized.

DESCRIPTION OF SYMBOLS 1 Optical amplification element 1a Reflective end 1b Non-reflective end 2 Lens 3 Narrow-band wavelength selector 4 Wavelength selector 5 Half mirror 6 Lens 7 Optical fiber 8 Optical mixer 9 Laser beam 10 Millimeter wave, submillimeter wave 20 Branch device 21 Optical mixer 22 etalon controller 23 etalon rotation drive device

Claims (7)

A multi-wavelength laser light source having an external resonator configuration;
A narrowband wavelength selector installed on the optical path in the external resonator, a wavelength selector, a selection wavelength variable means for changing a selection wavelength of the wavelength selector, and an optical mixer,
The multi-wavelength laser light source is a light source that outputs laser light having a plurality of spectral lines in a band from 50 GHz to 3 THz from the center of the spectrum of output light,
The wavelength selector is an optical filter that selects laser light from the multi-wavelength laser light source in a comb-like shape with respect to wavelength,
The narrow-band wavelength selector is for selecting two spectral lines from the laser light selected in a comb shape,
The selection wavelength variable means acts to change the transmission wavelength band to the wavelength selector,
The optical mixer generates a predetermined electromagnetic wave from 50 GHz to 3 THz by mixing the laser light of the two spectral lines.
A millimeter-wave and submillimeter-wave generator using two-wavelength laser beam mixing. The wavelength selector is a one-stage or multistage rio filter provided in an optical resonator, and the rio filter is a tunable rio filter.
The birefringent plate used in the Rio filter has an incident surface perpendicular to the optical path in the external resonator, has two axes with different refractive indexes on the incident surface, and acts by the action from the selected wavelength variable means. The apparatus for generating millimeter waves and submillimeter waves by mixing two-wavelength laser light according to claim 1, comprising a configuration for manipulating the refractive index of the birefringent plate.   By obliquely crossing the incident surface of the laser beam to the narrow-band wavelength selector and its incident optical path, the polarization in the direction oblique to the incident optical path is attenuated compared to the polarization in the direction orthogonal to the incident optical path. 3. The millimeter wave and submillimeter wave generator by two-wavelength laser beam mixing according to claim 1 or 2, wherein   By detecting the intensity of the predetermined electromagnetic wave generated from 50 GHz to 3 THz and returning the detection signal to the selected wavelength variable means so that the intensity of the electromagnetic wave becomes a maximum or a predetermined value, The millimeter wave by two-wavelength laser light mixing according to any one of claims 1 to 3, wherein the transmission characteristic of the wavelength selector is made to follow the transmission characteristic of the narrowband wavelength selector. Submillimeter wave generator.   The two-wavelength laser light mixing according to any one of claims 1 to 4, wherein the multi-wavelength laser light source having a configuration of an external resonator uses a semiconductor laser element having a double hetero structure. Millimeter wave and submillimeter wave generator.   5. The multi-wavelength laser light source having a configuration of an external resonator uses a quantum well type semiconductor laser element, and the two-wavelength laser light mixing according to any one of claims 1 to 4 Millimeter wave and submillimeter wave generator.   The millimeter wave by two-wavelength laser light mixing according to any one of claims 1 to 4, wherein the multi-wavelength laser light source having a configuration of an external resonator uses a quantum dot laser element. Submillimeter wave generator.

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